U.S. patent application number 13/676485 was filed with the patent office on 2014-05-15 for electrical interconnect and method of assembling a rechargeable battery.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is GENERAL ELECTRIC COMPANY. Invention is credited to Bhat Radhakrishna BADEKILA, Kristopher John FRUTSCHY, Thomas R. RABER, William H. SCHANK, Alec Roger TILLEY.
Application Number | 20140134473 13/676485 |
Document ID | / |
Family ID | 50681993 |
Filed Date | 2014-05-15 |
United States Patent
Application |
20140134473 |
Kind Code |
A1 |
FRUTSCHY; Kristopher John ;
et al. |
May 15, 2014 |
ELECTRICAL INTERCONNECT AND METHOD OF ASSEMBLING A RECHARGEABLE
BATTERY
Abstract
An electrical interconnect is disclosed that includes an inner
conductive material having a top surface and a bottom surface; and
an outer conductive material different from the inner conductive
material, wherein the outer conductive material is clad on the top
and bottom surfaces of the inner conductive material, wherein the
electrical interconnect is configured to be secured to a first
terminal of a first electrochemical cell and a second terminal of a
second electrochemical cell. A method of manufacturing an
electrical interconnect is also disclosed.
Inventors: |
FRUTSCHY; Kristopher John;
(Schenectady, NY) ; BADEKILA; Bhat Radhakrishna;
(Mangalore, IN) ; TILLEY; Alec Roger; (Ashbourne,
GB) ; RABER; Thomas R.; (Schenectady, NY) ;
SCHANK; William H.; (Howell, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GENERAL ELECTRIC COMPANY |
Schenectady |
NY |
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
50681993 |
Appl. No.: |
13/676485 |
Filed: |
November 14, 2012 |
Current U.S.
Class: |
429/158 ;
219/121.14; 228/160; 228/179.1; 29/623.1; 439/887 |
Current CPC
Class: |
Y10T 29/49108 20150115;
H01M 2/32 20130101; H01M 2/202 20130101; H01R 13/03 20130101; Y02E
60/10 20130101 |
Class at
Publication: |
429/158 ;
439/887; 29/623.1; 228/160; 228/179.1; 219/121.14 |
International
Class: |
H01M 2/20 20060101
H01M002/20; H01M 2/30 20060101 H01M002/30 |
Claims
1. An electrical interconnect comprising: an inner conductive
material having a top surface and a bottom surface; and an outer
conductive material different from the inner conductive material,
wherein the outer conductive material is clad on the top and bottom
surfaces of the inner conductive material, wherein the electrical
interconnect is configured to be secured to a first terminal of a
first electrochemical cell and a second terminal of a second
electrochemical cell.
2. The electrical interconnect of claim 1, wherein the outer
conductive material comprises nickel and wherein the inner
conductive material comprises copper or a copper alloy.
3. The electrical interconnect of claim 2, wherein the second
conductive material comprises a copper-beryllium alloy.
4. The electrical interconnect of claim 1, wherein the first
conductive material comprises nickel or a nickel alloy and the
second conductive material comprises aluminum or an aluminum
alloy.
5. The electrical interconnect of claim 1, wherein the electrical
interconnect is manufactured by hot cladding the outer conductive
material to the inner conductive material.
6. The electrical interconnect of claim 1, wherein the electrical
interconnect is manufactured by cold cladding the outer conductive
material to the inner conductive material.
7. The electrical interconnect of claim 1 further comprising: a
corrosion resistant coating that encloses the inner conductive
material and the outer conductive material.
8. The electrical interconnect of claim 7, wherein the corrosion
resistant coating comprises at least one of electroplated nickel,
chrome, silver, gold, titanium, platinum, tantalum, or alloys
thereof.
9. The electrical interconnect of claim 1, wherein the electrical
interconnect has a thickness and wherein the outer conductive
material clad to the top surface and the bottom surface of the
inner conductive material is at least 10% of the thickness of the
electrical interconnect.
10. The electrical interconnect of claim 1, wherein the electrical
interconnect has an electrical resistance of no more than 0.5 ohms
at 300 degrees Celsius measured between a point of connection of
the interconnect with the first terminal of the first
electrochemical cell and a point of connection of the interconnect
with the second terminal of the second electrochemical cell.
11. A method of manufacturing an electrical interconnect
comprising: joining a first conductive material to a second
conductive material to form a hybrid strip; cutting the hybrid
strip to form a plurality of electrical interconnects; coating each
of the plurality of interconnects with a corrosion resistant
coating; and annealing each of the plurality of electrical
interconnects.
12. The method of manufacturing an electrical interconnect of claim
11, wherein the first conductive material comprises nickel or a
nickel alloy and where the second conductive material comprises
copper or a copper alloy.
13. The method of manufacturing an electrical interconnect of claim
11, wherein joining the first conductive material to the second
conductive material comprises welding the first conductive material
to the second conductive material with an electron beam weld or a
solid state weld.
14. A rechargeable battery comprising: a plurality of
electrochemical cells, each cell having a first terminal and a
second terminal; and a plurality of electrical interconnects, each
interconnect having a first portion secured to the first terminal
of one of the electrochemical cells, and a second portion secured
to the second terminal of a different one of the electrochemical
cells, wherein each of the plurality of electrical interconnects
comprise a sheet of an inner conductive material clad on opposite
sides with sheets of an outer conductive material, wherein the
inner conductive material is different than the outer conductive
material.
15. The rechargeable battery of claim 14, wherein the first
terminal of each electrochemical cell comprises a first conductive
material and the second terminal of each electrochemical cell
comprises a second conductive material different than the first
conductive material.
16. A method of assembling a rechargeable battery comprising:
providing a plurality of electrochemical cells, each cell having a
first terminal and a second terminal; providing a plurality of
electrical interconnects, each electrical interconnect having a
first portion configured to be secured to the first terminal of one
of the electrochemical cells, and a second portion configured to be
secured to the second terminal of a different one of the
electrochemical cells, wherein each of the plurality of electrical
interconnects comprise a sheet of an inner conductive material clad
with sheets of an outer conductive material, and wherein the inner
conductive material is different than the outer conductive
material; securing the first portion of one of the electrical
interconnects to the first terminal of said one of the
electrochemical cells; and securing the second portion of said one
of the electrical interconnects to the second terminal of said
different one of the electrochemical cells.
17. The method of assembling a rechargeable battery as claimed in
claim 16, wherein securing the first portion of said one of the
electrical interconnects to the first terminal of said one of the
electrochemical cells comprises welding the first portion to the
first terminal; and wherein securing the second portion of said one
of the electrical interconnects to the second terminal of said
different one of the electrochemical cells comprises welding the
second portion to the second terminal.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] Embodiments of the subject matter disclosed herein relate to
electrical interconnects for connecting a terminal of an
electrochemical cell of a rechargeable battery to a terminal of
another electrochemical cell of the rechargeable battery.
[0003] 2. Discussion of Art
[0004] Rechargeable batteries include a plurality of energy storage
cells connected in series by electrical interconnects.
Interconnects provide an electrical connection between the negative
terminal of one energy storage cell to the positive terminal of the
next energy storage cell in the series. The resistance of prior
interconnects has reduced the efficiency of rechargeable battery
systems and may have necessitated additional energy storage cells
to compensate for the losses introduced by the interconnects. In
addition, interconnects have been costly to manufacture due to the
high temperature and potentially corrosive environment that may
exist inside a rechargeable battery.
[0005] It may, therefore, be desirable to have an electrical
interconnect for use in a rechargeable battery that differs from
those that are currently available.
BRIEF DESCRIPTION
[0006] Presently disclosed is an electrical interconnect. In an
embodiment, the electrical interconnect includes a first portion
configured to be secured to a first terminal of a first
electrochemical cell, wherein the first portion comprises a first
conductive material, and a second portion configured to be secured
to a second terminal of a second electrochemical cell, wherein the
second portion comprises a second conductive material. The first
conductive material is different than the second conductive
material.
[0007] In another embodiment, the electrical interconnect includes
an inner conductive material having a top surface and a bottom
surface, an outer conductive material different from the inner
conductive material, wherein the outer conductive material is clad
on the top and bottom surfaces of the inner conductive material.
The interconnect is configured to be secured to a first terminal of
a first electrochemical cell and a second terminal of a second
electrochemical cell.
[0008] In another embodiment, a method of manufacturing an
electrical interconnect includes providing a sheet of a first
conductive material having a top surface and a bottom surface, and
cladding the top surface and the bottom surface of the first
conductive material with a second conductive material to form a
clad sheet, wherein the second conductive material is different
than the first conductive material. The method further comprises
cutting the clad sheet into a plurality of electrical
interconnects, coating each of the plurality of electrical
interconnects with a corrosion resistant coating, and annealing
each of the plurality of electrical interconnects.
[0009] In another embodiment, a method of manufacturing an
electrical interconnect includes joining a first conductive
material to a second conductive material to form a hybrid strip,
cutting the hybrid strip to form a plurality of electrical
interconnects, coating each of the plurality of interconnects with
a corrosion resistant coating, and annealing each of the plurality
of electrical interconnects.
[0010] In another embodiment, a method of assembling a rechargeable
battery includes providing a plurality of electrochemical cells,
each cell having a first terminal and a second terminal, and
providing a plurality of electrical interconnects, each electrical
interconnect having a first portion and a second portion. The first
portion of each of the electrical interconnects comprises a first
conductive material and the second portion of each of the
electrical interconnects comprises a second conductive material
different than the first conductive material. The method further
includes securing the first portion of one of the electrical
interconnects to a first terminal of one of the electrochemical
cells, and securing the second portion of said one of the
electrical interconnects to a second terminal of a different one of
the electrochemical cells.
[0011] In another embodiment, a rechargeable battery includes a
plurality of electrochemical cells, each cell having a first
terminal and a second terminal, and a plurality of electrical
interconnects, wherein each electrical interconnect comprises a
first portion secured to the first terminal of one of the
electrochemical cells, and a second portion secured to the second
terminal of a different one of the electrochemical cells. The first
portion of each of the electrical interconnects comprises a first
conductive material and the second portion of each of the
electrical interconnects comprises a second conductive material
different than the first conductive material.
[0012] In another embodiment, a method of assembling a rechargeable
battery includes providing a plurality of electrochemical cells,
each cell having a first terminal and a second terminal, and
providing a plurality of electrical interconnects, each
interconnect having a first portion configured to be secured to the
first terminal of one of the electrochemical cells, and a second
portion configured to be secured to the second terminal of a
different one of the electrochemical cells. Each of the plurality
of electrical interconnects comprises a sheet of an inner
conductive material clad with sheets of an outer conductive
material, wherein the inner conductive material is different than
the outer conductive material. The method further comprises
securing the first portion of one of the electrical interconnects
to the first terminal of said one of the electrochemical cells, and
securing the second portion of said one of the electrical
interconnects to the second terminal of said different one of the
electrochemical cells.
[0013] In another embodiment, a rechargeable battery includes a
plurality of electrochemical cells, each cell having a first
terminal and a second terminal. The rechargeable battery further
comprises a plurality of electrical interconnects, each
interconnect having a first portion secured to the first terminal
of one of the electrochemical cells, and a second portion secured
to the second terminal of a different one of the electrochemical
cells. Each of the plurality of electrical interconnects comprises
a sheet of an inner conductive material clad on opposite sides with
sheets of an outer conductive material, wherein the inner
conductive material is different than the outer conductive
material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Reference is made to the accompanying drawings in which
particular embodiments and further benefits of the invention are
illustrated as described in more detail in the description below in
which:
[0015] FIG. 1 is a perspective view of an electrical interconnect
in use with electrochemical cells of a rechargeable battery;
[0016] FIG. 2 is a perspective view of an embodiment of an
electrical interconnect;
[0017] FIG. 3 is a perspective view of another embodiment of an
electrical interconnect;
[0018] FIG. 4 is a cross-section of the electrical interconnect of
FIG. 2 along section line 4-4.
[0019] FIG. 5 is a top view of a hybrid strip for manufacturing
electrical interconnects;
[0020] FIG. 6 is a cross-section view of another embodiment of an
electrical interconnect that includes a coating;
[0021] FIG. 7 is a cross-section view of an embodiment of a clad
electrical interconnect;
[0022] FIG. 8 is a graph of total cell resistance including the
interconnect for an embodiment of an electrical interconnect
according to the present disclosure and a prior art nickel
interconnect;
[0023] FIG. 9 is a test setup for measuring voltage drop across a
selection of interconnects; and
[0024] FIG. 10 is a graph of voltage vs. position at fixed
electrical current from for a prior art mild steel interconnect and
several embodiments of an electrical interconnect according to the
present disclosure.
DETAILED DESCRIPTION
[0025] The subject matter presently disclosed relates to a low
resistance electrical interconnect for connecting a terminal of an
electrochemical cell of a rechargeable battery to a terminal of
another electrochemical cell of the rechargeable battery. Referring
to FIGS. 1 through 10, embodiments of an electrical interconnect
are illustrated. A rechargeable battery may be constructed from a
wide variety of electrochemical cells, such as sodium-halide,
sodium-sulfur, lithium-sulfur, and other available electrochemical
cells used for energy storage. In one embodiment, the
electrochemical cells have an operating temperature determined by
the melting point of the materials utilized in the cells. For
example, the operating temperature may be greater than about 100
degrees Celsius, such as between (and including) 250 degrees
Celsius and 400 degrees Celsius, or between (and including) 400
degrees Celsius and 700 degrees Celsius, but other desired
operating temperature are also possible.
[0026] In some embodiments, the electrochemical cells (sometimes
referred to as energy storage cells) can have dimensions of about
37 mm.times.27 mm.times.240 mm, any of which dimensions may vary by
up to +/-50%, in accordance with various embodiments. In other
embodiments, the dimensions of the energy storage cell may vary as
desired to support the electrochemical cell for a given
application. In embodiments, the chemistry of a cell is of the
sodium-metal-halide type, in which NaCl and Ni are converted to Na
and NiCl.sub.2 during battery charging. The energy capacity of a
cell can range from about 30 amp*hours to about 250 amp*hours.
[0027] To provide greater energy storage capacity and greater
output voltage, a rechargeable battery often includes a plurality
of electrochemical cells connected in series. Electrical
interconnects are used to connect the positive terminal of one
electrochemical cell to the negative terminal of the next
electrochemical cell in the series. In embodiments, an electrical
interconnect includes a first portion configured to be secured to a
first terminal of a first electrochemical cell and a second portion
configured to be secured to a second terminal of a second
electrochemical cell. The first portion and the second portion of
the electrical interconnect are each formed of a conductive
material, however, the conductive material of the first portion is
different that the conductive material of the second interconnect.
In some embodiments, an electrical interconnect constructed of
different conductive materials may be referred to as a hybrid
interconnect.
[0028] Referring now to FIG. 1, an embodiment of an electrical
interconnect 10 is illustrated in use with a first electrochemical
cell 16 and a second electrochemical cell 18. For purposes of
illustration, only one interconnect 10 is illustrated, however, in
a rechargeable battery having a plurality of cells connected in
series, plural interconnects 10 connect the cells to one another in
series, with the first and last cells typically connected to a bus
bar or otherwise connected to the external terminals of the
rechargeable battery. That is, a first electrical interconnect
connects a second terminal (e.g., negative terminal) of a first
cell to a first terminal (e.g., positive terminal) of a second
cell, a second electrical interconnect connects a second terminal
of the second cell to a first terminal of a third cell, and so
on.
[0029] The first electrochemical cell 16 includes a cell housing 20
having cell walls 21 and a terminal body 22 secured to the cell
housing to retain the components of the electrochemical cell. In
some embodiments, the cell housing is electrically conductively
connected to one of the terminals of the electrochemical cell. In
other embodiments, the housing is insulated from the cell
terminals. The second electrochemical cell 18 similarly includes a
cell housing 30 having cell walls 31 and a terminal body 32 secured
to the cell housing.
[0030] The first electrochemical cell 16 and the second
electrochemical cell 18 each include a first terminal and a second
terminal. In embodiments, the first terminal of each cell is the
negative terminal, while the second terminal is the positive
terminal. In other embodiments, the first terminal may be the
positive terminal while the second terminal is the negative
terminal of the cell. In one embodiment, the first terminal 23, 33
of the cells extends from a peripheral edge of the respective
terminal body 22, 32. As shown on the second electrochemical cell
18, the first terminal 33 may include a first tab 34 and a second
tab 35. In this manner, the first terminal 33 is electrically
conductively connected to the terminal body 32, the cell walls 31,
and the cell housing 30. In embodiments, the first terminal 33,
terminal body 32, and cell housing 30 of the electrochemical cell
is formed of a steel, such as mild steel. Steel provides a variety
of benefits including mechanical strength for the cell housing,
terminal body, and first terminal, as well as a relatively low cost
as compared to other conductive materials.
[0031] As shown on the first electrochemical cell 16, the second
terminal 26 of the first electrochemical cell 16 may extend through
an aperture 28 in the terminal body 22 such that the second
terminal 26 is electrically isolated from the terminal body 22 and
the first terminal 23 of the cell. In embodiments, the second
terminal 26 may further include a closure cap 27 configured to
close the electrochemical cell such that the cell chemistry is
retained in the cell after assembly of an individual cell. Some
embodiments of electrochemical cells may also include a sealable
vacuum port such that the interior of the cell may be substantially
evacuated prior to sealing of the cell. In embodiments, the second
terminal 26, which may include a closure cap 27, is formed of a
nickel, such as nickel-201, or a nickel alloy. Nickel and nickel
alloys are reliably weldable to a variety of materials facilitating
assembly of the rechargeable battery.
[0032] The electrical interconnect 10 includes a first portion 12
and a second portion 14 as illustrated in FIG. 1. The first portion
12 of the electrical interconnect 10 is secured to the first
terminal 23 of the first electrochemical cell 16. The second
portion 14 of the electrical interconnect 10 is secured to the
second terminal 26 of the second electrochemical cell 18. In this
manner, the electrical interconnect 10 connects the electrochemical
cells in series as part of a string of electrochemical cells that
make up a rechargeable battery.
[0033] A rechargeable battery may be used in wide range of
applications and in a range of operating environments. Vibrations,
shocks, and other disturbances tend to generate movement of the
electrochemical cells within the rechargeable battery that stress
the interconnects. In various embodiments, to ensure a reliable
connection between the electrical interconnect and the
electrochemical cells, the first portion 12 is welded to the first
terminal, and the second portion 14 is welded to the second
terminal 36 during the assembly of the rechargeable battery. A
variety of weld processes may be used to secure the interconnect to
the first terminal and/or second terminal. In embodiments, the weld
is created by a laser weld process, a resistance weld process, an
electron beam weld process, a plasma arc weld process, a tungsten
inert gas weld process, a wire weld process, a solder weld process,
or any other appropriate welding technique. As used herein, the
term "welding" may also include sonic or ultrasonic welding, or
solid state welding. Moreover, the electrical interconnect may be
bent or deformed depending upon the configuration of the terminals
of the electrochemical cells to be connected to provide additional
bending stiffness or provide clearance inside the battery
compartment. As shown in FIG. 1, the electrical interconnect 10 is
shaped to provide clearance over the edge of the cell housing while
maintaining a substantially planar interface for welding the
interconnect to the first terminal and the second terminal of the
electrochemical cells.
[0034] Referring now to FIGS. 2-4, embodiments of electrical
interconnects 40 are illustrated. The electrical interconnect 40
includes a first portion 42 configured to be secured to a first
terminal of a first electrochemical cell, and a second portion 44
configured to be secured to a second terminal of a second
electrochemical cell. The first portion. The electrical
interconnect 40 is formed of at least two different conductive
materials joined by a seam 46. In an embodiment, the first portion
42 is formed of a first conductive material while the second
portion 44 is a second conductive material different than the first
conductive material.
[0035] In embodiments, the shape of the electrical interconnect is
adapted based on the configuration of the terminals of the
electrochemical cells to be connected. In one embodiment, an
electrical interconnect 40 has a substantially rectangular
configuration, such that the width of the first portion 42 and the
width of the second portion 44 are substantially uniform along the
length of the interconnect. In some embodiments, a substantially
rectangular configuration may provide a lower total resistance for
the electrical interconnect providing improved performance of a
rechargeable battery using the electrical interconnect. In
embodiments, the electrical interconnect 40 may be further adapted
to conform to the geometry of the terminals of the electrochemical
cells. An electrical interconnect 40 may include an aperture 48 in
the first portion 42. The aperture 48 may be configured to receive
a portion of a first terminal. In one embodiment, a first terminal
may include a pin that extends into the aperture 48 to assist in
positioning the electrical interconnect during assembly of the
rechargeable battery. In other embodiments, the electrical
interconnect 40 may include an aperture 50 in the second portion
44. The aperture 50 may be configured to receive at least a portion
of a second terminal. In one embodiment, a closure cap, such as
illustrated in FIG. 1, may be received in the aperture 50 before
the second portion 44 is secured to a second terminal of the
electrochemical cell, such as by welding.
[0036] Referring now to FIG. 3, another embodiment of an electrical
interconnect 60 is illustrated having a generally trapezoidal
shape, in which the width of the interconnect tapers along the
length, such that the second portion 64 of the interconnect has a
narrower width than the first portion 42. The first portion 62 is
joined to the second portion 64 by a seam 66, and the electrical
interconnect may be provided with, or without, apertures as
previously discussed. A trapezoidal shape may facilitate placement
of the electrical interconnect if one of the terminals of the
electrochemical cell has less clearance than the other
terminal.
[0037] Referring now to FIG. 4, a cross-section of the electrical
interconnect 40 of FIG. 2 is illustrated. The electrical
interconnect is formed of two different conductive materials joined
by a seam 66. In embodiments, the first portion 42 is formed of
nickel, such as nickel-201, or a nickel alloy. Nickel and nickel
alloys are reliably weldable to a variety of materials, including
steel such as may be used in housing and first terminal of an
electrochemical cell. While nickel and its alloys are reliably
weldable and corrosion resistant, they provide greater electrical
resistance reducing the efficiency of a rechargeable battery. In
other embodiments, the first portion 42 may formed of nichrome,
chromium, chromium alloys, or other metals that are weldable to
steels. In embodiments, an electrochemical cell has a mild steel
case which forms one of the terminals of the cell. An electrical
interconnect having a nickel portion may be welded to the mild
steel of the cell case providing a reliable weld to the cell case
and the second portion of the electrical interconnect. In this
manner, the materials of the electrical interconnect may be
selected to facilitate manufacture of a rechargeable battery while
reducing losses associated with the interconnect. To facilitate
assembly of a rechargeable battery, the length of the first portion
may be selected to provide a sufficient amount of the first
conductive material to form a reliable weld to a first terminal of
an electrochemical cell. In an embodiment, the length of the first
portion 42 is from 10% to 50% of the overall length of the
electrical interconnect as measured between a first end and a
second end. In other embodiments, the length of the first portion
42 is from 10% to 30% of the overall length of the electrical
interconnect.
[0038] The second portion 44 of the interconnect is formed of a
different electrically conductive material than the first portion
42. In embodiments, the second portion 44 is formed of copper.
Copper is highly conductive but subject to corrosion, particularly
when exposed to battery liquid electrolyte at elevated temperatures
such as may occur within a rechargeable battery. In another
embodiment, the second portion is formed of a copper-beryllium
alloy. In one embodiment, the copper-beryllium alloy includes
approximately 0.4% by weight beryllium, such as between 0.3% and
0.5%. In another embodiment, the copper-beryllium alloy includes
1.9% by weight beryllium, such as between 1.8% and 2.0%. In other
embodiments, a copper-beryllium alloy may include between 0.2% and
2.5% by weight beryllium. A copper-beryllium alloy provides
improved conductivity as compared to nickel or nickel alloys, and
also provides improved corrosion resistance and mechanical yield
strength as compared to pure copper. For example, the
copper-beryllium alloy having 1.9% by weight beryllium may have a
conductivity approximately 17% that of pure copper, while the alloy
having 0.4% by weight beryllium may have a conductivity
approximately 51% that of pure copper. Both alloys, however, are
substantially more resistant to corrosion than pure copper and
therefore better suited for use within rechargeable batteries where
the internal temperatures may be 300 degrees Celsius or more. In
yet other embodiments, the second portion 44 may be formed of
aluminum or aluminum alloys having a desired conductivity for a
given operating temperature range.
[0039] The first portion 42 is joined to the second portion 44 by a
seam 46. In an embodiment, the seam 46 is a weld seam formed by an
electron-beam weld process. The seam 46 has a width 88, such as
illustrated in FIG. 4. It has been found that an electron-beam weld
joining a first portion 42 of nickel to a second portion 44 of a
copper-beryllium alloy provides improved electrical conductivity.
In an embodiment, the electron-beam weld process partially melts
the nickel and copper-beryllium alloy adjacent the seam 46
resulting in the metals joining with reduced mixing of the
material. Mixing of materials in a welded seam has been found to
increase electrical resistance. By reducing the mixing of the
nickel and copper-beryllium alloys through the use of an
electron-beam weld process, an electrical interconnect is created
with desirable electrical resistance properties. In addition, an
electron beam weld process may provide a narrow seam 46. In one
embodiment, the weld seam 46 is no greater than 2.0 millimeters in
width. In another embodiment, the weld seam 46 has an average width
of less than 2.0 millimeters over the length of the seam. In other
embodiments, the seam 46 may have an average width of no more than
0.5 millimeters over the length of the seam. As used herein, the
width 88 of the seam may be measured as indicated in FIG. 4 and may
be measured along the length of the seam which defines the junction
between the first portion 42 and the second portion 44 of the
electrical interconnect. In other embodiments, the seam 46 is
formed by an ultrasonic weld process to create a solid state weld.
In a solid state weld, the mixing of material between the first
portion and the second portion may be substantially reduced
providing a desired electrical conductivity for the assembled
interconnect.
[0040] A process of manufacturing electrical interconnects is also
disclosed. Referring now to FIG. 5, a first material 72, such as
nickel, may be joined to a second material 74, such as the
copper-beryllium alloys previously discussed, in a strip as
illustrated in FIG. 5. The first material 72 may be joined to the
second material 74 to form a hybrid strip 70 of a desired length.
The length of the hybrid strip 70 produced may depend upon the
capabilities of the manufacturing equipment, however, fabrication
of longer strips may result in a more economical production
process. The hybrid strip 70 may be rolled to reduce the thickness
of the strip to a desired thickness 90 (see FIG. 4) for the
electrical interconnects. In one embodiment, an electrical
interconnect has a thickness 90 of approximately 1.2 millimeters,
such as between 1.0 millimeters and 1.4 millimeters. In another
embodiment, an electrical interconnect has a thickness 90 of
approximately 2.0 millimeters, such as between 1.8 millimeters and
2.2 millimeters. In yet other embodiments, an electrical
interconnect has a thickness 90 of between 1.0 and 2.2 millimeters.
The thickness 90 of the electrical interconnect, in combination
with the width and shape, may be selected to provide a desired
electrical resistance for the materials used. In addition, the
thickness 90 may be selected to facilitate the manufacturing
process. By reducing the thickness of the electrical interconnect,
the ability to weld the interconnect to the terminals of the
electrochemical cells may be improved. The hybrid strip 70 may be
stamped or cut to form individual electrical interconnects in the
shape and configuration desired for a given application. In some
embodiments, after being formed into the desired configuration the
electrical interconnect is annealed to improve the strength of the
interconnect and specifically the seam.
[0041] Referring now to FIG. 6, in yet another embodiment, an
electrical interconnect 100 includes a first portion 102 of a first
conductive material and a second portion 104 of a second conductive
material. Electrical interconnects are used inside rechargeable
batteries where operating temperatures may exceed 300 degrees
Celsius or more over many months or years while the battery is in
service. In an embodiment, an electrical interconnect 100 further
includes a corrosion resistant coating 106 over the first portion
102 and the second portion 104 to protect the electrical
interconnect from oxidation and/or corrosion within the
rechargeable battery. In one embodiment, the corrosion resistance
coating is electroplated nickel deposited over the interconnect to
protect the second portion from corrosion. Some prior interconnects
were formed entirely of nickel to reduce oxidation and corrosion
related problems, however, the reduced conductivity of nickel as
compared to copper or copper alloys resulted in reduced performance
of rechargeable battery systems. By providing a nickel coating to
limit corrosion, the second portion 104 of the electrical
interconnect 100 may be formed of a highly conductive material,
such as copper or a copper alloy that might not otherwise be
useable in the operating environment within a rechargeable battery.
In other embodiments, a corrosion resistant coating may include
chromium, silver, gold, titanium, platinum, or tantalum.
[0042] Referring now to FIG. 7, another embodiment of an electrical
interconnect 110 is disclosed. The electrical interconnect 110
includes a first end 116 configured to be secured to a first
terminal of a first electrochemical cell, and a second end 118
configured to be secured to a second terminal of a second
electrochemical cell. In this manner, the electrical interconnect
functions in a similar manner to the embodiments previously
discussed. The electrical interconnect 110 further includes an
inner conductive material 112 extending between the first end and
the second end, and an outer conductive material 114 at least
partially covering the inner conductive material. The outer
conductive material 114 is a different material than the inner
conductive material 112. In various embodiments, the outer
conductive material 114 is clad onto the inner conductive material
to form the electrical interconnect.
[0043] The electrical interconnect 110 may be formed by hot or cold
rolling a sheet of the inner conductive material between sheets of
the outer conductive material. The outer conductive material may
substantially cover a top and bottom surface of the inner
conductive material. In embodiments, the outer conductive material
may also cover the sides of the inner conductive material, such
that the inner conductive material is fully enclosed in the outer
conductive material. In other embodiments, the inner conductive
material may be exposed along the edges particularly when the
materials are joined in a rolling operation and then cut or stamped
to the desired size and shape. In either case, the electrical
interconnect 110 includes three layers, with the outer conductive
material 114 forming the outer layers and the inner conductive
material forming the middle layer.
[0044] In embodiments, the inner conductive material 112 may be
copper or a copper-beryllium alloy. As previously discussed, copper
and some copper alloys are susceptible to oxidation and/or
corrosion when used inside rechargeable batteries. Moreover, copper
and copper alloys may be difficult to weld to steel or other
materials used in the terminals of electrochemical cells. In other
embodiments, the inner conductive material 112 may be aluminum or
an aluminum alloy or other highly conductive metals suitable for
use in a given application. The outer conductive material 114, such
as nickel, is provided to protect the inner conductive material
from oxidation and corrosion. The outer conductive material 114
further improves the manufacturability of the rechargeable battery
as nickel and nickel alloys are reliably weldable to many materials
including steels. In other embodiments, the outer conductive
material may be chromium or a chromium alloy. In embodiments, the
electrical interconnect 110 may further includes a coating, such as
the corrosion resistant coatings previously discussed. In one
embodiment, an electrical interconnect is formed by hot or cold
rolling sheets of the inner and outer conductive materials, to form
a hybrid sheet having three layers. The hybrid sheet is then cut to
the shape and configuration desired for the electrical
interconnect. In some embodiments, the inner conductor may remain
exposed along the cut edges. In other embodiments, the electrical
interconnect is coated with a corrosion resistant coating, such as
electroplated nickel, to provide protection to the inner conductive
material that might otherwise be exposed along the edges of the
interconnect. In many embodiments, the corrosion resistant coating
is formed by the same conductive material used in outer conductive
material.
[0045] The thickness of the inner and outer conductive materials
may be selected to achieve a desired electrical and mechanical
performance for the electrical interconnect. In one embodiment, the
inner material is copper having a thickness of approximately 0.4
millimeters, and the outer material is nickel having a thickness of
0.4 millimeters on each side of the inner material. In another
embodiment, the inner material is copper having a thickness of
approximately 0.6 millimeters, and the outer material is nickel
having a thickness of 0.3 millimeters on each side of the inner
material. In various embodiments, the thickness of each sheet of
the outer conductive material is at least 10% or at least 20% of
the overall thickness of the electrical interconnect. By providing
sufficient outer conductive material, the electrical interconnect
may maintain its low resistance, corrosion resistance and weldable
properties when the first end and the second end of the
interconnect are welded to the terminals of electrochemical
cells.
[0046] Embodiments of the presently disclosed electrical
interconnects may provide improved electrical performance
characteristics as compared to prior designs. Referring now to FIG.
8, the performance of a prior pure nickel interconnect (designated
Ni) is compared to an interconnect constructed substantially as
shown in FIG. 2, having a first portion of nickel and a second
portion of a copper-beryllium alloy (designated CuBe). Each
interconnect was tested during discharge of a rechargeable battery
at 140 watts per cell constant power and the string resistance was
monitored during the discharge operation. As shown, for a given
amp-hour (Ah), the string resistance is reduced when using the CuBe
interconnect as compared with the prior Ni interconnect. Moreover,
the time at power was increased from 12.1 to 15.6 minutes.
Embodiments of the electrical interconnect presently disclosed may
result in savings greater than two watts per cell. For rechargeable
batteries having tens or hundreds of cells, the power savings
afforded may be substantial.
[0047] Referring now to FIGS. 9 and 10, the electrical performance
of several electrical interconnects is compared and illustrated.
The resistance of four electrical interconnects was measured at
22.degree. C. using a fixed 75 Amp current and a test setup as
illustrated in FIG. 9. The voltage drop across each of the
electrical interconnects was measured from a reference location
(designated as "ref") to each of three locations as generally
depicted. Referring to FIGS. 1 and 9, the "ref" location generally
corresponds to the connection point between the interconnect and
the first terminal of the electrochemical cell, and the location
designated "3" correspond to the point of connection between the
interconnect and the second terminal of the electrochemical cell.
The first interconnect tested was formed of mild steel and
represents a prior interconnect used in some rechargeable battery
systems. The second interconnect includes a first portion of nickel
and a second portion of copper-beryllium alloy as previously
discussed. The third and forth electrical interconnects tested each
include an inner conductive material of copper (Cu) and an outer
conductive material of nickel (Ni) having the thicknesses as
illustrated in the table below. As shown in the table, and depicted
in FIG. 10, each of the three hybrid electrical interconnects
performed better than the mild steel interconnect as demonstrated
by the reduced voltage drop and corresponding reduced electrical
resistance at each of the three test locations.
TABLE-US-00001 CuBe as Ni--Cu--Ni Ni--Cu--Ni mild steel rolled
(0.4-0.4-0.4 mm) (0.3-0.6-0.3 mm) mV mV mV mV reference 0 0 0 0
position-1 7.5 5.7 2.6 2.5 position-2 14.1 10.7 4.6 3.2 position-3
16 12.1 5.4 3.7 mOhm mOhm mOhm mOhm position-1 0.100 0.076 0.035
0.033 position-2 0.188 0.143 0.061 0.043 position-3 0.213 0.161
0.072 0.049
[0048] The presently disclosed electrical interconnects provide
substantially reduced resistance increasing the efficiency of a
rechargeable battery. At operating temperatures within a
rechargeable battery, such as 300.degree. C., the resistance of the
electrical interconnects increases. For example, the mild steel and
other prior art interconnects may have resistance well in excess of
0.5 ohms at the elevated temperatures within a rechargeable battery
resulting in the increased losses and reduced time at power
illustrated in FIG. 8. In embodiments, the electrical interconnects
presently disclosed provide a lower resistance at these elevated
temperatures. In one embodiment, the presently disclosed electrical
interconnect may have a resistance of less than 0.5 ohms. In other
embodiments, the presently disclosed electrical interconnect may
have a resistance of less than 0.200 ohms, which is less than the
resistance of a prior art mild steel interconnect even at lower
temperatures. The reduced resistance of the electrical interconnect
may be achieved by selecting conductive materials having lower
resistance and/or a lower coefficient of resistance. In addition,
the portion of each conductive material may be varied to further
improve the overall resistance achieved at the battery operating
temperature, such as by varying the size of the first portion or
the thickness of the outer conductive material as previously
discussed.
[0049] By reducing resistance and the corresponding power losses, a
rechargeable battery may be constructed using the presently
disclosed electrical interconnects using fewer electrochemical
cells while maintaining the same output voltage and power. An
electrical interconnect according to the present disclosure may
also provide desirable electrical, mechanical, and corrosion
resistance properties for use in a rechargeable battery. In this
manner, the electrical interconnects may improve the performance of
rechargeable batteries as compared to those that are currently
available.
[0050] The electrical interconnects presently disclosed may be used
to assemble rechargeable batteries having these improved
characteristics. In an embodiment, a method of assembling a
rechargeable battery includes providing a plurality of
electrochemical cells, each cell having a first terminal and a
second terminal; providing a plurality of electrical interconnects,
each interconnect having a first portion configured to be secured
to the first terminal of one of the electrochemical cells, and a
second portion configured to be secured to the second terminal of a
different one of the electrochemical cells, wherein the first
portion of each of the electrical interconnects is formed of a
first conductive material and the second portion of each of the
electrical interconnects is formed of a second conductive material
different than the first conductive material; securing the first
portion of one of the electrical interconnects to the first
terminal of said one of the electrochemical cells; and securing the
second portion of said one of the electrical interconnects to the
second terminal of said different one of the electrochemical cells.
Methods such as these may be used to assemble a rechargeable
battery that includes a plurality of electrochemical cells, each
cell having a first terminal and a second terminal; and a plurality
of electrical interconnects, in which each electrical interconnect
includes a first portion secured to the first terminal of one of
the electrochemical cells, and a second portion secured to the
second terminal of a different one of the electrochemical cells.
The first portion of each of the electrical interconnects is a
first conductive material and the second portion of each of the
electrical interconnects is a second conductive material different
than the first conductive material. In some embodiments, the first
terminal of each electrochemical cell is formed of a third
conductive material and the second terminal of each electrochemical
cell is formed of a fourth conductive material different than the
third conductive material. In one embodiment, the third conductive
material may comprise steel and the fourth conductive material may
comprise nickel or a nickel alloy. In another embodiment, the first
portion and the second portion of the interconnect are secured to
the terminals of the electrochemical cells by welding as previously
discussed.
[0051] In another embodiment, a method of assembling a rechargeable
battery includes providing a plurality of electrochemical cells,
each cell having a first terminal and a second terminal; providing
a plurality of electrical interconnects, with each interconnect
having a first portion configured to be secured to the first
terminal of one of the electrochemical cells, and a second portion
configured to be secured to the second terminal of a different one
of the electrochemical cells. Each of the plurality of electrical
interconnects is formed of a sheet of an inner conductive material
clad with sheets of an outer conductive material, in which the
inner conductive material is different than the outer conductive
material. The method also includes securing the first portion of
one of the electrical interconnects to the first terminal of said
one of the electrochemical cells; and securing the second portion
of said one of the electrical interconnects to the second terminal
of said different one of the electrochemical cells. Methods such as
these may be used to assemble a rechargeable battery having a
plurality of electrochemical cells, each cell having a first
terminal and a second terminal, and a plurality of electrical
interconnects, with each interconnect having a first portion
secured to the first terminal of one of the electrochemical cells,
and a second portion secured to the second terminal of a different
one of the electrochemical cells. In embodiments, each of the
plurality of electrical interconnects is formed of a sheet of an
inner conductive material clad on opposite sides with sheets of an
outer conductive material, where the inner conductive material is
different than the outer conductive material. In some embodiments,
the first terminal of each electrochemical cell is formed of a
first conductive material and the second terminal of each
electrochemical cell is formed of a second conductive material
different than the first conductive material.
[0052] In the specification and claims, reference will be made to a
number of terms that have the following meanings. The singular
forms "a", "an" and "the" include plural referents unless the
context clearly dictates otherwise. Approximating language, as used
herein throughout the specification and claims, may be applied to
modify any quantitative representation that could permissibly vary
without resulting in a change in the basic function to which it is
related. Accordingly, a value modified by a term such as "about" is
not to be limited to the precise value specified. In some
instances, the approximating language may correspond to the
precision of an instrument for measuring the value. Similarly,
"free" may be used in combination with a term, and may include an
insubstantial number, or trace amounts, while still being
considered free of the modified term. Moreover, unless specifically
stated otherwise, any use of the terms "first," "second," etc., do
not denote any order or importance, but rather the terms "first,"
"second," etc., are used to distinguish one element from
another.
[0053] As used herein, the terms "may" and "may be" indicate a
possibility of an occurrence within a set of circumstances; a
possession of a specified property, characteristic or function;
and/or qualify another verb by expressing one or more of an
ability, capability, or possibility associated with the qualified
verb. Accordingly, usage of "may" and "may be" indicates that a
modified term is apparently appropriate, capable, or suitable for
an indicated capacity, function, or usage, while taking into
account that in some circumstances the modified term may sometimes
not be appropriate, capable, or suitable. For example, in some
circumstances an event or capacity can be expected, while in other
circumstances the event or capacity cannot occur--this distinction
is captured by the terms "may" and "may be."
[0054] This written description uses examples to disclose the
invention, including the best mode, and also to enable one of
ordinary skill in the art to practice the invention, including
making and using any devices or systems and performing any
incorporated methods. The patentable scope of the invention is
defined by the claims, and may include other examples that occur to
one of ordinary skill in the art. Such other examples are intended
to be within the scope of the claims if they have structural
elements that do not different from the literal language of the
claims, or if they include equivalent structural elements with
insubstantial differences from the literal language of the
claims.
* * * * *